The Molded Polystyrene Manufacturing Process

1. Pre-Expansion and Aging

The raw material resin used to manufacture polystyrene is received in the form of small beads ranging from 0.5 to 1.3mm in diameter. These small beads are formulated and manufactured by the suppliers to contain a small percentage of the naturally occurring gas pentane. This gas is impregnated throughout the body of each small bead. The pre-expansion phase of manufacturing is simply the swelling of the small bead to almost 50 times its original size through the heating and rapid release of the gas from the bead during its glass transition phase.

ACH Foam Technologies uses very sophisticated technology and equipment in its pre-expansion processes. By utilizing a computer-controlled weighing system, a measured amount of beads are introduced into the expansion equipment. Steam is introduced into the vessel and an agitator mixes the expanding beads as the heat in the steam causes the pentane to be released from the beads. A level indicator tells the computer when the desired specified volume has been reached. After a pressure equalization phase, the expanded beads are released into a bed dryer and all condensed steam moisture is dried from the surface. The pre-expansion is complete and another cycle is ready to run. This process takes approximately 200 seconds to finish.

After the expanded beads have been dried, they are blown into large open storage bags for the aging process. The beads have been under a dynamic physical transformation that has left them with an internal vacuum in the millions of cells created. This vacuum must be equalized to atmospheric pressure, otherwise this delicate balance may result in the collapse or implosion of the bead. This process of aging the expanded beads allows them to fill back up with air and equalize. This aging can take from 12 to 48 hours, depending on the desired expanded density of the bead. After the aging is finished, the beads are ready to be molded into blocks.

ACH Foam Technologies' high-tech molding equipment goes one step further after the pressure is released by submitting the newly formed block to a partial vacuum which allows for a faster cooling period. This added step pulls residual moisture from the block resulting in a drier, better-fused block of polystyrene. The block is then ejected from the mold and another cycle is ready to run.

2. Curing

Heat curing is the next step in ACH's process. Heat not only accelerates the curing process of the freshly molded blocks, but also assures that the material is dimensionally stable. Heat provides a completely dry material for the best fabrication results. We have developed unique heat rooms for this purpose, which are designed for efficient inventory transitions. This is allows ACH to offer the highest level of service and fastest response time possible.

3. Molding Process

The molding process involves taking the loose expanded beads and forming them into a solid mass. ACH Foam Technologies' shape & block molded products are formed using a state-of-the-art vacuum-assisted mold. By utilizing a system of load cells, the computer is capable of controlling the exact weight of beads introduced into the mold cavity. Once the cavity is filled, the computer uses a vacuum system to evacuate residual air from the material. The vacuum is relieved by live steam, which flows over the entire mass of beads in the cavity. This vacuum-rinsing process softens the polymer structure of the bead surface and is immediately followed by the pressurization of the mold cavity with more live steam. The latent heat from the steam and subsequent pressure increase cause the beads to further expand. Since this is a confined environment, the only way the beads can expand is to fill up any voids between them causing the soft surfaces to fuse together into a polyhedral-type solid structure. The computer releases the pressure after it reaches its predetermined set point. The loose beads are now fused into a solid mass.

4. Shape Molding

The shape molding process is essentially the same as block molding except that the product is molded into its specific final shape using a custom mold rather than a large 16’ x 4’ x 36” block mold in which the polystyrene block requires additional trimming and cutting to reach its intended size & shape. Shape molded products are typically used for packaging, insulated concrete forms, lost foam foundry patterns and OEM products.

5. Fabrication

ACH Foam Technologies utilizes a series of thermal hot-wire cutting tools to accomplish a smooth surface while still maintaining strict quality control of dimensional tolerances. These tools heat the wires electrically and their resistance characteristics cause them to reach heat levels from 400° F to 800° F. The wires are drawn down through the block to achieve the length and width cuts, and then the blocks are pushed through the hot wires via a conveyor to achieve the desired thickness.